Gregory first studied medicine under his father Aaron, who embraced Christianity, and was probably baptized in his youth. This accounts for his not being conversant with Hebrew, though he was well acquainted with Jewish doctrines.

He was successively Bishop of Guba(1246), of Lakaba (1247), and of Aleppo (1253). In 1264 he was named Maphrian, head of the Syriac Orthodox Church in the East, with his seat at Tikrit on the Tigris.

Gregory was a prolific writer on theology, philosophy, ethics, history, grammar, medicine, mathematics and astronomy. Some of his works were written in Arabic, but most of them in Syriac. He was the last great Syriac writer, though he is important rather as a collector than as an independent writer. He is best known for his Syriac grammar, "Ketaba de Semhe," his "Chronicle" in two parts, ecclesiastical and political; his "Menarat Kudshe," a compendium of theology, philosophy, medicine, physics and metaphysics, and his scholia on the Old and the New Testament (Auzar Raze). In the last-named he occasionally cites readings from the Samaritan text; it is interesting to note that in a scholium to 2 Kings xvii. 28, he says: "The Law (i.e. text of the Pentateuch) of the Samaritans does not agree with that of the Jews, but with the Septuagint. He occasionally cites opinions of the Jews, e.g., on Ps. viii. 2, on the Shem Hamephorash (the name Jehovah). In the introduction to his commentary on Job he mentions as a writer the priest Asaph (brother of Ezra the Scribe), who identifies Job with Jobab. In speaking of the Apocryphal account of the death of Isaiah, he cites "one of the Hebrew books" as authority. (Nestle Marginalien ii. 48).